The red, green and blue (RGB) color model involves combining different proportions of red, blue and green light to produce other colors. This model is used in many different types of color displays, such as cathode-ray-tube monitors, liquid crystal displays, and plasma-based displays. In the typical color display, each pixel is configured to combine varying amounts of red, green and blue to create a wide range of colors. The 1931 CIE color space, created by the International Commission on Illumination in 1931, is a useful and convenient way to determine the range of colors available based on specific red, blue and green wavelengths. An example set of RGB wavelengths is λR=630 nm, λG=532 nm and λB=465 nm, respectively.
Each type of color display uses some kind of light source to generate red, blue and green light. Such light sources include, for example, high-intensity discharge (HID) lamps used in combination with red, green and blue filters; separate red, blue and green lasers (e.g., laser diodes); and one or more lasers where the laser light is converted to different wavelengths via non-linear effects.
Non-laser-based RGB sources have several shortcomings, including lack of directionality, relatively low brightness, and relatively low conversion efficiency due to their broad spectral band. Also, such broad-band (i.e., “white light”) sources are limited by a flat power vs. wavelength curve. If one tries to use extreme wavelengths on the red or blue end of the spectrum to obtain good color map coverage, a great deal of light in the middle of the spectrum needs to be thrown away to achieve a proper tint. This translates into poor wall-plug efficiency. Conversion efficiency can be improved, but at the expense of color map coverage, which means fewer available colors for the display.
Laser-based RGB sources can have high-directionality and relatively high brightness, but typically require a large laser or a number of different lasers. For those laser-based RGB light sources that include one or two lasers, the designs are relatively complex and non-compact. In particular, for those laser-based RGB light sources that use non-linear optical elements (i.e., non-linear crystals), it is important for cost reduction, compactness and overall commercial viability to reduce the number of lasers and non-linear elements.